Synthetic plastics account for the use of 7% of fossil fuels in the world. The limited resources and rising price of fossil fuels present a challenge to seek developing renewable resources for manufacturing of “green” plastics. However, applications of renewable polymers lag significantly behind petrochemical-derived polymers, partially because of limitations in the monomer resources and the derived polymers with controlled properties.
Rosin (including gum rosin, wood rosin and tall rosin) is an exudate from pine trees and other plants. The major components of rosin are resin acids: primarily abietic acid (AA) and levopimaric acid. The presence of a carboxyl group and/or conjugated double bonds in their structures imparts them tunable chemical reactivity: e.g. derivation of a vinyl group. Rosin and its derivatives, produced millions of tons annually, are generally used as ingredients for inks, vanishes, adhesives, paper size, cosmetics, medicines, chewing gums, etc. Some of them are used as additives or modifying agents for the improvement of the properties of synthetic polymers. However, the use of rosin as renewable resources for the preparation of well-defined synthetic polymers (e.g. homopolymers and block copolymers) has not yet been explored. The major reason behind this is that most rosin based polymers are prepared by step growth polymerization or free radical polymerization that lack controls on the polymer structures at molecular level, molecular weight, molecular weight distribution and functionality. The absence of the tunability of these parameters limits these polymers used for broader and promising alternatives to petroleum based polymers such as thermoplastic resins, thermoplastic elastomers, polymeric varnishes, polymeric wax, adhesives, coatings, printing inks to shape memory polymers, polymer nanocomposites, pharmaceutics, anti-fouling materials, etc.
As such, a need exists for well-defined rosin-derived polymers with controllable molecular weight, low polydispersity and varied chemical topologies and chain functionality.